1. Field of the Invention
The present invention relates to perhalogen-aromatic compounds without any hydrogen atoms and a method for producing the same. More particularly, the present invention relates to 1,4-bis(bromodifluoromethyl)tetrafluorobenzene and a method for producing the same in a high yield.
2. Description of Related Art
Halogen-containing aromatic compounds, especially those have substituted by a difluoroalkyl group or a bromodifluoroalkyl group, their polymerization products have excellent properties such as thermal and chemical resistance, water repellent, low-dielectric constant, low reflectivity and so on.
Recently, among commercial fluorine-containing aromatic compounds, poly(tetrafluoro-p-xylene) represented by the following formula (1) has been widely applied to dielectric films in the electronics and coating industries due to its excellent processability. Products coated with poly(tetrafluoro-p-xylene) have excellent properties such as anticorrosion, moisture-proofness, electrics insulation, and the coating films are ultrathin, transparent, and pinholeless.

1,4-bis(bromodifluoromethyl)benzene (BFB) represented by the following formula (2) is an important precursor for preparing poly(tetra-fluoro-p-xylene).

BFB is mainly obtained by reacting α,α,α′,α′-tetrafluoro-p-xylene (TFPX) with a brominating agent, N-bromosuccinimide (NBS). Currently, the method for synthesizing BFB is to dissolve TFPX and NBS in CCl4 solvent, and then to reflux the mixture under UV irradiation to obtain BFB in a yield of 50 to 80%. Alternatively, BFB also can be obtained by using Br2 instead of NBS to brominating TFPX (for example, the addition of Br2 into the reaction solution was divided in several times at 80° C. under visible-light irradiation of 390 to 500 nm).
Since the dielectric constant of fluorine-containing poly-p-xylene decreases as the amount of fluorine atoms increases in the molecule, the polymer formed from precursor, 1,4-bis(bromodifluoromethyl)tetrafluorobenzene (BFTFB), can predictably have a lower dielectric constant than poly(tetra-fluoro-p-xylene).
Commonly, BFTFB can be synthesized in a similar manner of synthesizing BFB, but the starting material for bromination is 1,4-bis(difluoromethyl)tetrafluorobenzene (DFMTFB) instead of TFPX.
However, in the synthesis of BFTFB mentioned above, there are several disadvantages in that: (1) the brominating agent, NBS, decomposes rapidly at high temperature under UV irradiation or initiator condition, and is usually used at reaction temperature below 100° C.; (2) Br2 easily evaporates and loses under reflux at 80° C. due to its low boiling point, hence the amount of Br2 used usually raises to several times more than the theoretical amount thereof and it is difficult to perform the bromination at temperature higher than 80° C.; (3) most polymers and metals can't resist the corrosive effect of bromine, only very limited materials capable of being used as a reactor.
Furthermore, because the starting material, 1,4-bis(difluoromethyl)tetrafluorobenzene (DFMTFB), has four fluorine atoms on benzene ring, the strong electronegativity makes the molecule unusually chemical stable and incapable of being brominated under above-mentioned conventional bromination condition. As a result, it is understood that a higher temperature condition is necessary for provision of higher energy than the conventional method to synthesize 1,4-bis(bromodifluoromethyl)tetrafluorobenzene (BFTFB).